This invention relates generally to the ignition of a gas generant such as used for the inflation of inflatable devices such as airbag cushions used in inflatable restraint systems for vehicle occupants. In particular, the invention relates to such an ignition material which, upon combustion, produces or results in a relatively large amount of gaseous products.
It is well known to protect a vehicle occupant using a cushion or bag, e.g., an "airbag cushion," that is inflated or expanded with gas when the vehicle encounters sudden deceleration, such as in the event of a collision. In such systems, the airbag cushion is normally housed in an uninflated and folded condition to minimize space requirements. Such systems typically also include one or more crash sensors mounted on or to the frame or body of the vehicle to detect sudden decelerations of the vehicle and to electronically trigger activation of the system. Upon actuation of the system, the cushion begins to be inflated in a matter of no more than a few milliseconds with gas produced or supplied by a device commonly referred to as an "inflator."
Many types of inflator devices have been disclosed in the art for the inflating of one or more inflatable restraint system airbag cushions. Inflator devices which form or produce inflation gas via the combustion of a gas generating material, i.e., a "gas generant," are well known. It is also known that certain of such inflator devices may use such generated gas to supplement stored and pressurized gas by the addition of high temperature combustion products, including additional gas products, produced by the burning of the gas generating material to a supply of the stored, pressurized gas. In some cases, the combustion products produced by the burning of a gas generating material may be the sole or substantially the sole source for the inflation gas issuing forth from a particular inflator device.
It is common that inflator devices include an initiator, such as a squib, and an igniter. In practice, upon receipt of an appropriate triggering signal from a crash or other selected deceleration sensor, the initiator activates causing the rapid combustion of the igniter material, which, in turn, ignites the gas generant.
Commonly desired features or performance criteria for inflatable restraint system igniter compositions include:
1. ignitability via typical squib charges such as by means of primary explosives such as zirconium/potassium perchlorate or lead trinitroresorcinate, for example; PA1 2. upon combustion, having a high heat of explosion; PA1 3. ease and safety of manufacture and production; PA1 4. exhibit minimal or reduced ignition delays, e.g., ignite a gas generant composition within an inflator device within about 10 milliseconds, preferably within about 8 milliseconds or less and, even more preferably, at least in certain applications, within about 5 milliseconds or less; and PA1 5. produce or result in relatively low levels of various undesirable effluent gases such as nitric oxide (NO), ammonia (NH.sub.3) and carbon monoxide (CO), for example. PA1 about 10 to about 25 composition weight percent of boron fuel; PA1 about 55 to about 80 composition weight percent of an oxidizer component; and PA1 about 10 to about 25 composition weight percent of an organic gas-producing fuel component.
Typical igniter compositions used in such applications are composed of a metallic fuel and selected oxidizer. Common useful metallic fuels for such compositions include boron, zirconium, titanium and silicon, for example. Typical or common oxidizers used in such compositions include alkali metal perchlorates, chlorates and nitrates. One such igniter formulation common or standard for use in airbag inflators is composed of about 15 to about 30 weight percent (typically about 25 weight percent) boron and about 70 to about 85 weight percent (typically about 75 weight percent) potassium nitrate. In the art, this standard igniter formulation is commonly referred to as "BKNO.sub.3."
Unfortunately, typical igniter compositions, such as BKNO.sub.3, are generally deficient in one or more of the above-identified criteria. Further, such typical igniter compositions may commonly burn at very high combustion temperatures, such as temperatures of up to about 3000 K. Also, the gas fraction produced by reaction of such igniter compositions is generally relatively low.
Thus, there is a need and a demand for an igniter composition and method of inflation gas generation which are generally more effective in satisfying one or more of the above-identified performance criteria. In particular, there is a need and a demand for an igniter composition and method of inflation gas generation which may more satisfactorily simultaneously fulfill multiple, and preferably each, of such performance criteria.
At the present time, sodium azide is a commonly accepted and used gas generating material. While the use of sodium azide and certain other azide-based gas generant materials meets current industry specifications, guidelines and standards, such use may involve or raise potential concerns such as involving handling, supply and disposal of such materials.
In addition, economic and design considerations have also resulted in a need and desire for alternatives to azide-based pyrotechnics and related gas generants. For example, interest in minimizing or at least reducing overall space requirements for inflatable restraint systems and particularly such requirements related to the inflator component of such systems has stimulated a quest for gas generant materials which provide relatively higher gas yields per unit volume as compared to typical or usual azide-based gas generants. Further, automotive and airbag industry competition has generally lead to a desire for gas generant compositions which satisfy one or more conditions such as being composed of or utilizing less costly ingredients or materials and being amenable to processing via more efficient or less costly gas generant processing techniques.
As a result, the development and use of other suitable gas generant materials have been pursued. In particular, efforts have been directed to the development of azide-free pyrotechnics for use in such inflator device applications. For example, U.S. Pat. Nos. 5,592,812 and 5,673,935, the disclosures of which are incorporated herein in their entirety, relate to certain metal complexes for use as gas generants. Such complexes are described as including a cationic metal template, sufficient oxidizing anion to balance the charge of the complex, and a neutral ligand containing hydrogen and nitrogen. In particular, disclosed are certain gas generant compositions which are at least essentially azide-free and which contain a metal ammine complex having a metal cation of a transition metal or an alkaline earth metal.
While these patents state that it is possible to initiate combustion reaction of these complexes by conventional igniter devices such as which include a quantity of BKNO.sub.3 pellets, in practice it has been found sometimes difficult to ignite such gas generants using such conventional igniter compositions.
Thus, there is a need and a demand for igniter compositions which are effective for the igniting of various gas generant materials. In particular, there is a need and a demand for igniter compositions of improved effectiveness in the igniting of gas generants such as or similar to those described above.